本文所探討的重點是以Nordhaus（1975）的模型為出發，來分析內閣制政治景氣循環。由Nordhaus模型的假設，引進不確定因素Ω（t），以動態最適控制的方法來求得內閣制下失業率的最適控制路徑u*（t），並且將兩者的結論作比較，解釋其經濟意涵。內閣制鑑的政治景氣循環會比總統制下（Nordhaus）的政治景氣循環具有較高的選舉頻率、較低的振幅。此外，就社會福利的觀點來看，對於選民面對兩種類型的政治景氣循環時，其福利變化的優劣，乃是取決於選民的偏好。

Based upon Nordhaus’ model, we can analyze the political business cycle (PBC) of a parliamentarian system. In this paper, by adding the uncertainty factor to Nordhaus’ assumptions, we can obtain the unemployment rate of optimal control path by using the dynamic optimal control theory. Comparing these two results wit hNordhaus’ original findings, the model of political business cycle of parliamentarian system has higher elective frequency and lower amplitude in the unemployment rate of optimal control path than that of president system. From the social welfare point of view, which is better is decided by voter preference when voters face these two types of PBC. The article also uses a similar model to analyze the PBC during the period of New Economy and Great Depression. By using the concept of sub-optimal policy, we can determine the government’s unemployment rate of optimal control path.

政治景氣循環; 內閣制; 最適控制理論; 最適控制路徑; 不確定因素; 次最適

Political Business Cycle (PBC);Parliamentarian System;The Optimal Control Theory; The Optimal Control Path; Uncertain Factor; Sub-optimal